1. Field of the Invention
This invention relates to field emission devices and, more particularly, to a method of fabricating field emitters useful in displays.
2. State of the Art
Cathode ray tube (CRT) displays, such as those commonly used in desk-top computer screens, function as a result of a scanning electron beam from an electron gun impinging on phosphors on a relatively distant screen. The electrons increase the energy level of the phosphors. When the phosphors return to their normal energy level, they release the energy from the electrons as a photon of light, which is transmitted through the glass screen of the display to the viewer. One disadvantage of a CRT is the depth of the display required to accommodate the raster scanner.
Flat panel displays have become increasingly important in appliances requiring lightweight portable screens. Currently, such screens use electroluminescent or liquid crystal technology. Another promising technology is the use of a matrix-addressable array of cold cathode emission devices to excite phosphor on a screen, often referred to as a field emitter display.
Spindt et al. discusses field emission cathode structures in U.S. Pat. Nos. 3,665,241, 3,755,704, and 3,812,559. To produce the desired field emission, a potential source is provided with its positive terminal connected to the gate or grid and its negative terminal connected to the emitter electrode (cathode conductor substrate). The potential source is variable for the purpose of controlling the electron emission current.
Upon application of a potential between the electrodes, an electric field is established between the emitter tips and the low potential anode grid, thus causing electrons to be emitted from the cathode tips through the holes in the grid electrode.
The clarity or resolution of a field emission display is a function of a number of factors, including emitter tip sharpness. The process of the present invention is directed toward the fabrication of very sharp cathode emitter tips.
One aspect of the process of the present invention involves forming sharp asperities useful as field emitters. The process comprises patterning and doping a silicon substrate. The doped silicon substrate is anodized. Where the silicon substrate was doped, regions of very sharply defined spires of porous silicon are formed. These sharp spires or asperities are useful as emitter tips.
Another aspect is fabrication of emitter tips using porous silicon. The method comprises blanket doping and anodizing a silicon substrate. The unmasked, anodized substrate is then exposed to patterned ultraviolet light. The exposed areas are oxidized in air. The oxidized areas are either stripped with hydrofluoric acid or retained as an isolation mechanism.
A further aspect of the present invention is the sharpening of field emitters. The method comprises anodizing existing silicon emitters, thereby causing the emitters to become porous. The porous silicon tips are exposed to ultraviolet light and rinsed with a hydrogen halide. The ultraviolet light oxidizes the tips and they become sharper as the oxide is stripped.
Other features and advantages of the present invention will become apparent to those of skill in the art through a consideration of the ensuing description, the accompanying drawings, and the appended claims.